Document function behavior completely

/**
 * Returns a diagnostic message for ECMAScript module syntax errors
 * in CommonJS files under verbatimModuleSyntax.
 *
 * @param node - The AST node where the error occurred
 * @returns A DiagnosticMessage explaining the error. If the file has a .cts or .cjs extension,
 *          a specific error message for CommonJS files is returned. Otherwise, a more general
 *          error message with suggestions for resolving the issue is returned.
 * @throws {SyntaxError} If the node type is invalid for module syntax checking
 * @deprecated Use getModuleDiagnostic() instead
 */
function getVerbatimModuleSyntaxErrorMessage(node: Node): DiagnosticMessage {
    // Skip validation for non-module files to improve performance
    const sourceFile = getSourceFileOfNode(node);
    const fileName = sourceFile.fileName;
    // ...
}